1. Field of the Invention
The present invention relates to the manufacture of a cellular vitreous material and, more particularly, relates to a method and apparatus for leveling a batch of pulverulent constituents in making a vitreous cellular material.
2. Description of the Prior Art
Cellular vitreous materials are well known for there use as heat insulators and for other similar applications. An example of a cellular vitreous material is cellular glass formed by heating a pulverulent glass batch which includes a cellulating agent, such as carbon black or the like, to a temperature permitting sintering and cellulation of the batch as described in U.S. Pat. No. 2,736,142. Additionally, examples of vitreous cellulatable siliceous materials formed from a pulverulent constituent batch are also disclosed in U.S. Pat. No. 2,736,142.
In one method of making a vitreous cellular material, the batch of pulverulent constituents, such as a cellulatable glass batch, is placed in a mold as, for example, a generally rectangular mold, and heated to preselected sintering and cellulating temperatures. Gases are generated in the heated mass and are entrapped in the mass in bubble form to give the mass a cellular structure. A block of vitreous cellular material, such as cellular glass, is removed from the mold and annealed.
The sintering temperature is the temperature at which the particles of the pulverulent batch become soft and adhere together. The cellulation of the batch of pulverulent constituents, such as a pulverulent glass batch, generally results at a temperature around or slightly above the sintering temperature. In the preparation of a vitreous cellular material from a pulverulent batch of constituents, a major concern is the uneven sintering and cellulating of the pulverulent constituent batch leading to the formation of a nonuniformly cellulated material. The nonuniform cellulation can be present in the form of voids, folds, or the like. Further, a top surface geometry that is not substantially uniform would promote decreased selection rates. Maintaining a uniformity of cell geometry in the formed vitreous cellular material promotes maximum insulating efficiency, if the vitreous cellular material is used in insulating applications. Further, the higher the degree of uniformity present in the batch of pulverulent constituents prior to sintering and cellulating of the batch, the more likely it is that the pulverulent constituent batch will reach cellulating temperature faster and in a more uniform manner; and the more likely it is that uniform cell geometry will be promoted in the formed vitreous cellular material. Promoting uniformity within the pulverulent constituent batch can promote increased production and selection rates for the resultant vitreous cellular material.
U.S. Pat. No. 2,736,142 to Baumler et al. discloses a process for manufacturing cellulated material. Baumler relates to the manufacture of cellular vitreous products, such as cellular glass and cellular silica, from pulverulent batch material. In Baumler, the pulverulent batch is initially formed into a number of small segments. The batch is segmented by scoring, dicing, separating, or other suitable methods which impart a segmented appearance to the batch. The segmentation of the batch can be uniform so as to produce a uniform cellulation or can be in a pattern resulting in a pattern of cellulation. The segmented batch is then heated to a temperature sufficient for the segments to sinter, cellulate, and expand through entrapment of gases generated therein to form a unitary structure.
Baumler et al. states that benefits achieved by segmenting the batch are relatively uniform and rapid heat penetration of the batch and a substantial uniformity of cell size within each piece, or segment, in relation to each other piece or segment.
U.S. Pat. No. 4,225,545 to Munk et al. discloses a method and apparatus for making preforms from a pourable substance for use in producing three-dimensional profiled articles. In Munk et al., a pourable substance is introduced into a container having a perforated bottom. The perforated bottom together with a mold defines a forming space to be filled with the pourable substance. The pourable substance proceeds through the perforations of the container bottom and is distributed throughout the forming space, resulting from vibration of the perforated container bottom. The pourable substance is compacted within the forming space due to the vibration of the perforated bottom. The preform can be taken out of the mold and compressed elsewhere into the profiled article, or the article can be produced from the preform directly in the mold. The bottom may also include two juxtaposed bottom members each having a different perforation spacing and each having an independent vibratory movement relative to each other.
Munk et al. states that the method disclosed therein is advantageous for producing preforms for articles of uniform wall thickness, even if the articles have a strongly profiled configuration and steep wall portions. If this is the case, Munk et al. states that vibratory movement to the perforated container bottom is substantially along a horizontal plane to compact the pourable substance in the forming space.
U.S. Pat. No. 3,965,527 to Zwart discloses a method and apparatus for filling spacing core materials, such as honeycomb. In Zwart's method, a compressible fibrous material is placed on a flat base and a sheet of rigid open cell core stock is placed on the fibrous material. A weight is placed over the open cell core stock. The base is vibrated until the lower edges of the core stock cut through the layer of fibrous material. The resulting cut portions of the fibrous material expand into the open cells of the core stock. The core stock is subjected to a partial vacuum from the top thereof to allow the cells of the core to uniformily fill with the cut fibrous material. A fine mesh screen desirably is placed over the core to prevent the compressible fibrous material from being drawn into the vacuum producing apparatus.
U.S. Pat. No. 3,697,208 to Munk et al. discloses an apparatus for filling molds. In Munk et al., non-flowing molding materials are blown into the mold cavity which has a screen defining one surface of the article to be molded. As the non-flowing molding materials fill up the cavity, the carrying air vents through the screen. When the mold cavity fills up to the feeding nozzle, a vent flap in the nozzle opens allowing the air carrying the non-flowing materials to vent through a screened opening exposed by the flap.
U.S. Pat. No. 3,171,872 to Jarrett et al. discloses a method and apparatus for producing particle board and the like. Jarrett discloses use of a vibratory conveyor unit having an open trough mounted on springs inclined at an angle from the vertical and extending upwardly from a base fixed to a traveling frame. The trough is provided with a wire mesh screen deck sized to allow separation of the fine and coarse particles. The particles are deposited on the vibratory conveyor unit from a belt scale. The finer particles pass through the wire screen deck and rest on the bottom of the trough, while the coarser particles are supported on the wire mesh screen deck. This patent notes that the wire mesh screen deck is removably supported in the trough to allow decks of different mesh sizes to be used. Additionally, Jarrett states that one or more screen decks can be used in the trough to provide the desired particle separation.
U.S. Pat. No. 2,689,597 to Kinnear discloses an apparatus and process for forming mats of comminuted material. In this patent, a reticulated member is interposed between a source of supply of the comminuted material and a receiving surface, the reticulated member having a mesh of a gauge adapted to pass the material. A relative transverse movement is imparted between the source of material and the receiving surface and the reticulated member is simultaneously vibrated to distribute the material on the receiving surface to uniform density. The reticulated member can be vibrated at high frequency and with a small amplitude of vibration.
U.S. Pat. No. 3,168,603 to Seefluth discloses a method and apparatus for preparing sheets of thermoresponsive plastic particulate material. In Seefluth's method for forming a sheet of thermoresponsive plastic particulate material, a plurality of substantially monogranular layers of the material are laid down in successive layers. After laying down each layer, a heat source is past over the just-laid-down layer causing the plastic particles to fuse and solidify with each other and with the earlier laid particles. Desirably, the plastic particulate material is subjected to vibration to promote uniform leveling of the material prior to heating.
U.S. Pat. No. 3,660,547 to Ruekberg discloses an electrostatic molding process. In Ruekberg's method for producing containers, a charged comminuted material is introduced into a channel having a similar electrical charge. The channel is positioned within a mold having a potential of opposite electrical charge. The material is agitated in the channel to assist in the electrostatic distribution of the comminuted material in the mold. The temperature of the mold is controlled to permit fusing of the deposited material in the form of a container. This patent mentions that a screen may be placed over the open portion of the channel to provide uniform distribution of the comminuted material.
Ruekberg further mentions that the comminuted material can be plastic, glass or metal which is induced to deposit on the mold surface under the influence of electrical means.
U.S. Pat. No. 3,746,589 to Reinke discloses a method of making bubble-free, fiber reinforced plastic laminates by tamping operations. In Reinke, a layer of fibrous material is tamped into a layer of liquid plastic material. The tamping is performed by directing blows on the layers in adjacent areas arranged like a grid, while the layers are moved relative to the areas. This patent mentions that the surface of the impulse transmitters, which exert the blows or tamping, may be perforated.
What is needed in the making of a vitreous cellular material from a batch of pulverulent constituents is a method and apparatus for leveling the batch of constituents which promotes substantially uniform compaction of and distribution within the pulverulent constituent batch allowing a faster sintering rate and substantially uniform cell geometry.
What is further needed is a method and apparatus for leveling a batch of pulverulent constituents in making a vitreous cellular material which generally eliminates the need for vibration of a mold pan into which a pulverulent batch of constituents is placed.